THE TOXICITY OF CERTAIN AMINO ACIDS FOR BRUCELLAE

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Abstract
Tryp-tophan and cystine were found to be highly toxic to Brucella abortus 1257 in a medium containing no other amino acids. Two additional amino acids, methionine and phenylalanine, were slightly toxic to this organism, whereas none of the other 15 amino acids of the casein digest series proved toxic at concns. well above those found in 1-2% casein digests. Only the cystine toxicity of this organism showed a persistence in the presence of other amino acids, which might implicate it as the antibrucella factor of casein and other digest media. Cystine toxicity for brucellae correlates in many respects the previously reported tryptose toxicity for these organisms. However, the authors are not yet sure whether the 2 are or are not identical. Forty-two strains of B. abortus showed markedly less tolerance for cystine than did 10 strains of B. suis. Acclimated strains of B. abortus tended to be less tolerant than CO2-requiring strains. Nine strains of B. melitensis were intermediate in their tolerance for cystine. The cystine content of certain synthetic media was shown to be responsible for the failure to obtain growth of some strains of B. abortus. Cysteine tended to give zonal inhibition of growth of B. abortus 1257. This zone was explained in terms of the balance between the tendency of cysteine to be oxidized to cystine and the toxicity-reversing effect of residual cysteine. Varying amts. of the reducing agent Na formaldehyde sulfoxylate restricted and, with increasing amts., eliminated the zonal toxicity of cysteine.